Hi, I made several changes to my Sky HD box. First thing i added was a Tacima Mains Conditioner (around £30). This added so much extra performance for all my kit including TV. Noticable difference in sound and picture quality. Then i tried several different HDMI cables, tried Chord Active, QED P, Thatcable settling on a Wireworld (£50). The cable really improved low bit rate channels such as the Music ones. Cable kept external noise at bay whilst delivering pristine quality signal, motion improved too, assuming consistency of signal delivery. These changes were good but i felt that little bit of extra noise in SD channels could be improved so i added a new Silver plated mains cable with Ferrite band (£35) to remove that little bit of noise, and add some extra shielding over the flimsy Sky lead. The difference in audio, picture contrast and motion have to be seen to be believed. The cable was from 'www.mains-cables-r-us.co.uk'. Just a warning that the silver takes a lifetime to burn in before you get the full benefit. Tried on PS3 too and great improvement to BD quality. Tried on TV too yet blurring became an issue so i still use included lead for that.
I have my Sky HD box set to 1080i and i calibrated my TV pic on an SD channel (news is good) with black and white background for contrast, whites used to test brightness, sharpness look at edges and take just below any drop in edge definition. Colours, look for red and avoid blurring. Basically when setting look for any negative effects on the edges of backgrounds presenters etc. on all picture tweaks. Take a step back to eliminate and you should be good to go. When i then went to HD it was perfect.
Best of all i can keep all my kit and use it on any other piece of equipment i choose, and get benefits for my TV and BD player too.